1. Field of the Invention
The present invention relates to a diaphragm with moving coil for an electrodynamic transducer. The diaphragm has in its center a spherically-shaped portion. A toroidally-shaped zone extending to the diaphragm edge is provided adjacent the spherically-shaped portion. The toroidally-shaped zone may be provided with corrugations.
2. Description of the Related Art
A diaphragm of the above-described type is used successfully in sound generators and sound receivers.
In the ideal case, a diaphragm of the above type should have the vibration behavior of a piston, so that vibration properties are obtained which are very similar to those of the spherical source of the 0th order. Accordingly, when manufacturing such a diaphragm, it is a particular object to realize this ideal case as closely as possible by the special selection of material and shape of the diaphragm.
Experience has shown that the vibration behavior of a diaphragm including a moving coil mass is characterized at higher frequencies of the transmission range of 20 kHz and above in that with increasing frequency the sensitivity of the electrodynamic transducer decreases steadily, wherein periodic fluctuations in the frequency pattern are observed in this frequency range. In the frequency range above approximately 5 to 8 kHz, the perception of the observer is that with increasing frequency the acoustically effective diaphragm surface area decreases continuously. This phenomenon is already mentioned in Austrian Patent 382 281.
It is well known that the deteriorating vibration behavior of the diaphragm at higher frequencies is due to the increase of effects caused in the diaphragm by flexural or bending waves. DE-AS 10 92 061 describes in detail how this type of natural vibrations can be eliminated in conical diaphragms.
Also, in dynamic transducers with a diaphragm of the above-described type it was attempted in the past to compensate as much as possible the loss of sensitivity occurring at high frequencies by utilizing a Helmholtz resonator. For this purpose, the natural resonance and quality of the resonator must be selected in such a way that the desired frequency pattern of the transducer is actually achieved. This was not always successful because it was not always possible to establish the band width and quality of the resonator to the extent required for an optimum compensation. Compromises had to be accepted or two-way systems had to be used.
Another proposal for improving the vibration behavior of diaphragms at higher and high frequencies can be found in British Patent No. 596 869. This proposal either refers to a sandwich-like coating of the diaphragm with a stiffening material or an embossment of the diaphragm with appropriate patterns to obtain a stiffening effect. However, these improvements are essentially only applicable to diaphragms having a certain shape and are not necessarily transferable to any type of diaphragm.